1. Field of the Invention
The present invention relates to a liquid crystal display device, or the like, used for a computer, word processor, etc., and also to a tape carrier package mounted on the display device which package includes a semiconductor chip for driving a display medium such as for example a liquid crystal material.
2. Description of the Related Art
FIG. 23 illustrates an example of a liquid crystal display device, which includes: a liquid crystal panel including an upper glass plate 15 and a lower glass plate 16 provided so as to interpose a liquid crystal material (not shown); a backlight unit 21 as a light source; a semiconductor chip 5 for driving the liquid crystal material; a tape carrier package (TCP) 7 connecting the semiconductor chip 5 to the wiring (or lines) provided on the lower glass plate 16; a printed board 23 for connecting a plurality of TCPs 7 together; and a vessel 22 for covering the liquid crystal panel.
Known methods for mounting a semiconductor chip for driving a liquid crystal material include: mounting the semiconductor chip directly on the liquid crystal panel; and mounting the semiconductor chip supplied in the form of a tape carrier package (TCP) on the liquid crystal panel.
In the latter method, as shown in FIG. 23, an electrode provided on the lower glass plate 16 and a patterned portion of a conductive material on the TCP 7 are attached together via an anisotropic conductive film (not shown) by thermo compression bonding, so as to provide a plurality of TCPs along the periphery of the liquid crystal panel. The plurality of TCPs 7 mounted around the liquid crystal panel are connected to the common printed board 23 which is provided with printed lines. Signals for conducting a display via the liquid crystal material are supplied to the TCPs 7 through the printed board 23. Moreover, conventionally, some chip components (e.g., a chip capacitor), are mounted on the printed board 23 if they cannot be included in the semiconductor chip 5. The vessel 22 is provided so as to surround the periphery of the liquid crystal panel.
The assembly steps for the liquid crystal display device include: connecting a liquid crystal driving output terminal of the TCP 7 to an electrode provided on the lower glass plate 16 via the anisotropic conductive film (not shown); and thereafter connecting an input signal terminal of the TCP 7 to the printed board 23 by soldering or via the anisotropic conductive film.
When a bendable TCP 25 is used, as shown in FIG. 24, the TCP 25 is bent after the above steps so that the printed board 23 matches the shape of the module.
On the other hand, the former method includes a Chip On Glass (COG) method, where the semiconductor chip 5 having metal bumps is mounted facing down directly onto the lines provided on the lower glass plate 16. There are different ways for making connections in this COG method such as: one described in Japanese Laid-open Publication No. 4-105331, etc., where connections are directly made by solder bumps after which the gap between the semiconductor chip and the glass plate is filled with a resin; and one described in Japanese Laid-open Publication Nos. 4-76929, 4-71246, 4-317347, etc., where, as shown in FIG. 25, the metal bumps of the semiconductor chip 5 are connected to the lines on the lower glass plate 16 via an anisotropic conductive film (ACF) 20 made of a resin (binder) 20b including conductive particles 20a. In the latter method, the resin (binder) 20b of the anisotropic conductive film 20 is used in place of the filling resin in the former method. Recently, the COG method using the anisotropic conductive film which can be easily repaired and which dose not require the resin filling has been widely used.
To each semiconductor chip used in the method where the printed board is used or in the COG method, input signals and power voltages are parallelly input through the lines provided on the printed board or by the ITO lines provided on the liquid crystal panel. However, chip select signals are synchronized with the clock signals parallelly input so that signals are transferred among the semiconductor chips.
In recent years, a prevailing technique is to ensure a larger display area for a certain module size by reducing the width by which the liquid crystal panel extends beyond the glass plate (i.e., the frame size). Moreover, the cost of a liquid crystal panel is higher than that of a CRT, and great cost reduction has been demanded for the liquid crystal panels.
Under such circumstances, as a method using a TCP, it has been proposed (Japanese Design Patent Application No. 2-40145) to use a slim-type TCP which is obtained by shaping a semiconductor chip into an elongated shape in order to reduce the width by which the TCP extends beyond the glass plate. Moreover, it has also been proposed (Japanese Laid-open Publication No. 2-132418, etc.) to reduce the frame size by bending a portion of the TCP which extends beyond the glass plate, as described above.
However, both of the proposed methods require the printed board, the TCP and the liquid crystal panel, and the assembly process thereof requires two connection steps, i.e., one for connecting the glass plate of the liquid crystal panel with the TCP, and another for connecting the TCP with the printed board. This increases material cost and the number of steps to be performed, thereby presenting a bottleneck in reducing the cost of a liquid crystal module.
Moreover, another method has been proposed (Japanese Laid-Open Publication No. 5-297394, Japanese Laid-Open Publication No. 6-258653, etc.) in which a liquid crystal display device includes the liquid crystal panel (reference numeral 15 in FIG. 26A denotes the upper glass plate of the liquid crystal panel) and the TCP 7 but does not include a printed board, as shown in FIG. 26A. In this method, as shown in FIG. 26B, adjoining two TCPs 7 are directly connected to each other, whereby input signals are transmitted/received through only the TCPs 7.
In the case of this proposed method, although it is possible to reduce the material cost for the printed board, two connection steps are required; one for connecting the glass plate of the liquid crystal panel with the TCP 7; and another for connecting the TCPs 7 together, thereby providing no cost reduction in terms of the number of steps to be performed. Moreover, in this proposed method, if one of the continuously connected TCPs 7 becomes defective, the defective one of the TCPs 7 has to be removed. Such a removal may give some mechanical damage to the adjacent TCPs 7, and may also present a burden on the process in terms of the number of steps to be performed, requiring disconnection at three positions (at the right and left input terminals and at an output terminal of the defective TCP 7). Moreover, since transmission/reception of input signals is all performed between the TCPs 7, the input terminals thereof need to be arranged respectively on the left and right sides, perpendicular to the side on which the output terminal thereof is provided. The input lines connected respectively to the input terminals will also have to be arranged, thereby increasing the width of the TCP 7, which may then conflict with the frame size limitation of the liquid crystal panel. Moreover, the increased area of the TCP 7 will result in an increased material cost. Thus, the proposed method has some difficulty in repair, does not reduce the number of connection steps; and increases the TCP size.
On the other hand, in the COG method, since the semiconductor chip is directly mounted on the glass plate, the packaging cost thereof is lower than that in a method using a TCP. Moreover, when input signals can be supplied to the semiconductor chip via the lines on the glass plate, the printed board may also be eliminated, thereby presenting a significant advantage in terms of cost. In such a case, there is another advantage that the mounting process is done only by mounting the semiconductor chip on the glass plate, thereby reducing the mounting cost.
However, in practice, the configuration as described above is only possible for a relatively small liquid crystal panel of up to about 3 to 6 inches, but is not possible for a currently-dominant large liquid crystal panel of about 10 inches or more. The reason therefor is that the sheet material used for the lines provided on the glass plate has a resistance, whereby the wiring resistance of the input signal lines cannot be suppressed to a low level. When the glass plate is small, the wiring length on the glass plate is short. However, when the glass plate is large, the wiring length on the glass plate is long, a voltage across the length on the glass plate drops, and a valid signal is not transmitted to the liquid crystal driving semiconductor chip.
Moreover, in view of the above-described wiring resistance, the wiring width on the glass plate may have to be increased even in a small liquid crystal panel, whereby the chip mounting area on the glass plate becomes wider than the TCP. Such an increase in the size of the glass plate may reduce the number of panels which can be produced from one mother glass, whereby the cost reduction may not be achieved in terms of the module as a whole.
A method (Japanese Laid-Open Utility Model Publication No. 4-77134, etc.) has been proposed as a countermeasure to the above problem. In the method, as shown in FIG. 27, a flexible wiring board 18 is provided on the lower glass plate 16 of the liquid crystal panel in the vicinity of the mounting portion of each semiconductor chip 5, and the lines of the flexible wiring board 18 are directly connected to the lines provided on the lower glass plate 16, whereby input signals are transmitted through the flexible wiring board 18. This method requires the flexible wiring board which corresponds to the printed board in the method using a TCP, whereby there is no advantage in terms of the cost and process.
Moreover, when using a printed board in a large-size liquid crystal panel, a stress is applied to the TCP due to the difference between a linear expansion coefficient of the printed board and a linear expansion coefficient of the glass plate. Consequently, wire breaks may occur in the TCP, thus lowering reliability. Another proposed method (Japanese Laid-Open Publication No. 8-15716) is to use, in place of the printed board, a substrate obtained by providing lines on a glass plate. However, this method also has a problem that the glass plate wiring substrate is costly, while the wiring resistance thereof is also higher than that of the printed board.
Furthermore, in the case of the COG method, since chips are provided as bare chips, a test is normally made when it is still in the form of a wafer, but no test will be made after it is diced into individual chips. Therefore, when the semiconductor chip is mounted on the glass plate, it is difficult to ensure the quality of the semiconductor chip (i.e., it is not a Known Good Die). Particularly, in the case of a large panel on which a large number of semiconductor chips are mounted, the repair rate is likely to increase, thereby possibly increasing the cost.
In the case of the COG method, or in the case of using the glass wiring substrate in place of the printed board, the resistance between the line for transmitting the input signal can be reduced by providing an aluminum line in the semiconductor chip. Thus, making it possible to reduce the chances of being transmitted an invalid signal because of low resistance in the input signal line. However, the employment of aluminum requires extension of the width of an internal line of the semiconductor chip. The internal line needs to be designed with a large width so that the semiconductor chip is able to flow large current and increase the reliability of the device. As a result of the width increase, a wiring region of the chip becomes large which in turn increases chip area. The increase in chip area results in material costs for the chip to increase. Additionally, by using the above method, a clock signal can not be transmitted, because the semiconductor generates noise which may influence the signal transmitted therethrough. For example, a clock signal being transmitted via the semiconductor chip may become corrupted by noise from the chip.
According to one aspect of this invention, a tape carrier package includes: a line provided on one surface of a tape substrate; and a semiconductor chip mounted on an other surface of the tape substrate, the semiconductor chip having an electrode which is electrically connected to the line. The line extends from one end to an opposite end of the tape substrate and includes a connection where an intermediate line portion provided in a middle between the ends is electrically connected to the electrode.
In one embodiment of the invention, the connection is formed to overhang substantially at a device hole provided in the tape substrate and is electrically connected to the electrode of the semiconductor chip substantially at the overhang portion.
In another embodiment of the invention, the intermediate line portion including the connection is formed to protrude so as to extend over the device hole; and the connection is in the portion overhanging substantially at the device hole.
In still another embodiment of the invention, the intermediate line portion formed to protrude is in one of an I shape and a U shape.
In still another embodiment of the invention, the device hole is provided as a notch substantially at a location over which the linearly-shaped intermediate line portion extends.
In still another embodiment of the invention, the intermediate line portion including the connection is bent in a V shape toward the device hole; and a portion of the intermediate line portion which extends substantially at the device hole is linearly shaped.
In still another embodiment of the invention, the linearly-shaped intermediate line portion which extends substantially at the notch is provided with a bent buffering portion.
In still another embodiment of the invention, the device hole is formed separately from other openings formed in the tape substrate; and the intermediate line portion is provided so as to run linearly substantially at the device hole.
In still another embodiment of the invention, the line is for a power source; and the tape substrate is further provided with a signal line to be electrically connected to the electrode of the semiconductor chip.
In still another embodiment of the invention, a plurality of the lines are provided on the tape substrate; and an electronic component different from the semiconductor chip is connected and mounted between the lines.
In still another embodiment of the invention, the semiconductor chip includes a buffer circuit for signal connection between the semiconductor chip and a semiconductor chip provided on an other tape carrier package.
In still another embodiment of the invention, the buffer circuit included in the semiconductor chip is formed by an input buffer circuit and an output buffer circuit.
In still another embodiment of the invention, the buffer circuit included in the semiconductor chip is formed by an input/output buffer circuit.
According to another aspect of this invention, a display device is provided, which includes the tape carrier package of present invention provided on a glass plate of a display panel. Adjoining ones of the tape carrier packages are electrically connected to one another via a line provided on the glass plate.
In one embodiment of the invention, an anisotropic conductive film is used for the connection between the line provided on the glass plate and the tape carrier package.
In another embodiment of the invention, the line provided on the glass plate is a line directly formed on the glass plate.
In still another embodiment of the invention, an electronic component different from the semiconductor chip is connected and mounted onto the line provided on the glass plate.
In still another embodiment of the invention, the display panel is a liquid crystal panel.
In still another embodiment of the invention, the line provided on the glass plate is a line formed on a substrate other than the glass plate.
In still another embodiment of the invention, an electronic component different from the semiconductor chip is connected and mounted onto the line provided on the glass plate.
Hereinafter, the function of the present invention will be described.
In the TCP of the present invention, the input terminals for the lines are provided on a side perpendicular to a side on which an output terminal is provided, whereby it is possible to ensure the quality of the semiconductor chip (i.e., it is possible to determine whether the chip is good or bad), by performing a test using the input terminal.
Moreover, in the display device of the present invention, the TCP including the input terminals is mounted on the display panel, where electrical connection between adjoining TCPs is achieved by the lines provided on the display panel. Therefore, the provision of the lines for input signals (which presents the most significant problem), is required only on the TCP and on the glass plate, whereby it is possible to reduce the material cost, and also to reduce the number of connection steps to be performed to ⅓ of that in the conventional technique, since the connection of the input/output terminals can be done in a single step of mounting the TCP. Therefore, a considerable cost reduction can be realized also in terms of the number of connection steps to be performed.
Moreover, according to the present invention, only a defective TCP needs to be removed from the glass plate, and only the surface of the glass plate has to be washed, whereby a repair process can be achieved with half the work of the conventional technique. Moreover, a portion of the TCP extending beyond the glass plate can be bent when mounting a bezel, and the like, whereby the frame size can also be reduced.
Since a printed board with a large linear expansion coefficient is not used, reliability against the temperature variation is improved as compared to the conventional technique. Moreover, mechanical reliability against vibration, or the like, can also be increased to a level comparable to that in the COG method, since there is no movable section or no section to be oscillated as compared to the TCP or the printed wiring board in the conventional TCP method.
Moreover, a bonding process to the glass plate is performed in a single step via the anisotropic conductive film. Since the lines on the TCP, the lines on the semiconductor chip, and the lines on the glass plate can be electrically connected to one another by the anisotropic conductive film, with which the function of the multi-layer lines of the conventional printed board can be replaced, and it is possible to transmit/receive input signals at a low wiring resistance without using a continuous large external substrate such as the flexible wiring board or the printed board.
Furthermore, by providing a buffer circuit in the semiconductor chip while not using the aluminum lines provided in the semiconductor chip, the wiring region inside the semiconductor chip can be reduced, and the chip area can also be reduced, whereby a reduced cost and an improved reliability can both be realized.
Furthermore, by transmitting the input signals via the buffer circuit within the semiconductor chip, it is possible to shape the waveform of the input signals, whereby the influence of the noise can be suppressed, and even signals which require a fast operation such as a clock signal can be reliably transmitted in a normal manner.
Furthermore, by providing the buffer circuit with a structure of an input/output buffer circuit, it becomes possible to freely and externally alter the signal transmission direction, whereby the semiconductor chip can be shared.
Thus, the invention described herein makes possible the advantages of (1) providing a tape carrier package in which the quality of a semiconductor chip can be easily ensured (i.e., it is possible to determine whether the chip is good or bad), before mounting the semiconductor chip; and (2) providing a display device using such a tape carrier package, in which the number of connection steps can be reduced, repair can be easily reformed, and the reliability thereof improved.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.